All cellular organisms respond to vibration, touch, gravity, or changes in osmolarity, but the molecular bases of such mechano-sensations are unknown. Candidate molecules include certain ion channels, such as the mechano-sensitive channel of very large conductance (MscL) of Escherichia coli observed by patch-clamp experiments. We used a functional test to identify MscL as a l7-kD protein and cloned the corresponding gene, mscL. The sequence indicates a unique protein of 136 amino acid, highly hydrophobic, and rich in P structure. We plan to find mscL homologues in other species and to define the conserved regions. We will then generate chimeras and site-directed mutants as well as selected mutants to define the amino-acid residues or peptide regions responsible for solute permeability and mechano-sensitivity. By combining recombinant DNA technology and patch-clamp analysis, we hope to understand the molecular structure/function relation of this unique mechanosensitive protein.